In data processing installations, host processors generally have a relatively large plurality of peripheral data storage devices for storing data to be used in connection with host processor operations. Each host processor generally executes programs that allocate portions of the data storage space of the respective peripheral data storage device to various computer processes within the host processor. When the data processing environment grows to have an extremely large number of addressable data storage volumes which are mounted on a data storage unit, such as a magnetic or optical library system, the utilization of such data storage space and the accessing of such data storage space becomes extremely complicated. Libraries are often used in a hierarchical storage system with the volatile memory units, such as integrated circuit storage devices, being at the top of the hierarchy and the library systems being at the bottom.
Often times, duplicate copies of the same data are stored in different levels of the hierarchy in order to promote the rapid access of data by the host central processing units. The use of cache memories, for instance, permits the rapid access of often-used data by placing the most recently accessed data and the data in the immediate area to the most recently accessed data into the cache memory. This copy of the data stored in a lower level of the hierarchy, such as in a direct access storage device, or a magnetic tape storage device, or in a library system, is copied into a faster access memory store. The duplication of the data in different memory locations is often used for the protection of the data in the event one of the storage areas fails. Generally though, the duplication of the data in the different levels of the storage areas in the hierarchy is for the rapid access to the data in what could be inordinate periods of time for data retrieval which could complicate the retrieval of data and the operation of the entire data processing system.
Some applications of data processing systems require the storing and retrieving of such large amounts of information that many storage devices are required. In these applications, the user typically requires a hierarchy of storage that includes some combination of main memory and one or more types of peripheral storage devices. The goal of the hierarchy is to obtain moderately priced, high capacity storage while maintaining high speed access to the stored information. Hierarchical storage typically allows information to be transferred between main memory and one or more of the peripheral storage devices or between one or more peripheral storage devices and one or more other peripheral storage devices. Further storage is provided by maintaining libraries of data storage media, such as tapes, magnetic disks, or optical disks that can be mounted onto the existing peripheral devices.
In the retrieval of data from the lowest level in the hierarchy, the library system, the delay grows to seconds rather than fractions of seconds. When the data processing environment grows to have an extremely large number of addressable data storage volumes, which are mountable in a library storage unit, the utilization of such data storage space and the accessing of such data storage space becomes extremely complicated. Improvements to the retrieval of the stored data can result in the saving of much time.
Data storage in data processing environments typically is viewed as a hierarchy of storage levels. The first, or fastest, level is the level that communicates directly with the host processors in the data processing environment. The lower levels of the hierarchy, which may be up to six, seven or eight levels, add increasingly large data storage capacities, but have increasingly longer access times. The lower levels of the storage hierarchy are often characterized by a plurality of individually addressable data storage devices stored in library systems. It is desired to utilize these various addressable storage devices in an optimal manner for enhancing the overall operation of the data processing environment and, particularly, the data storage hierarchy.
In a library environment, a single section of data stored on a single media casing, whether cartridge or cassette or disk unit, is mountable and demountable from a drive unit. Even in an automated library, the access time to one volume of data is measured in seconds; hence, it is a relatively long time with respect to the time base of a data processing environment. Accordingly, it is desirous to minimize the time required for access to a single media unit of data. It is likewise desirous to increase the efficiency of the retrieval of data stored in the volumes for operating the data storage hierarchy and, hence, the data processing system in a more efficient manner.
It is, therefore, an object of the present invention to provide an enhanced library storage subsystem and a method of operating the enhanced library storage subsystem.
It is another object of the present invention to provide a management of media units in a library system and the storage of data in each media unit in a manner which enhances the retrieval of data from the library system.
Yet another object of the present invention is to provide an apparatus and a method of operating a library system that improves the response time for retrieving data information stored in cartridges in the library system.